Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Patent
1992-07-09
1994-03-08
Sugarman, Scott J.
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
351160H, 351177, G02C 704
Patent
active
052931862
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a contact lens and in particular to ways of increasing the gas permeability of a contact lens.
A hard contact lens such as of polymethyl-methacrylate has advantages of longevity, biocompatability, strength, durability, wettability and the ability to mask up to a certain degree of astigmatism but has the drawback of effectively starving the cornea surface of oxygen. This leads to oedema (thickening of the cornea) and other undesirable effects.
A soft contact lens such as of a hydrogel has advantages of oxygen permeability and comfort but is in turn susceptible to accumulation of proteins and other deposits, and is required to be kept scrupulously clean and sterile.
The present invention proposes to combine these advantages as appropriate, by enhancing the oxygen permeability of any contact lens material.
DESCRIPTION OF THE PRIOR ART
To avoid oedema, it has been proposed in U.S. Pat. No. 3833786 to fenestrate a contact lens by holes sufficiently large for bulk tear flow to take place through them, thus transferring sufficient dissolved oxygen to the eye surface. This is expensive and difficult to achieve consistently and may impair the perceived clarity of the contact lens. Various techniques have been proposed for the fenestration of contact lenses. One system (U.S. Pat. No. 3,227,855) uses a spark to locally burn a small hole through the lens and others (U.S. Pat. No. 3,833,786 above and U.S. Pat. No. 3,971,910) describe laser based systems. The lasers described are of the CO.sub.2 type in which a concentrated beam is used to burn through the lens to produce the holes.
These patents start from the basis that the fenestration itself is to provide a path for tears to flow through the lens enabling fresh oxygenated tears to feed the cornea. Most experiments have accordingly been conducted on lenses with a few (generally less than 10) large diameter (generally greater than 200 microns) holes. Wichterle and Krejci (International Eyecare, September 1985 page 315) recommended contact lens perforation in the centre only, i.e. the optically most disadvantageous location. Hill & Leighton (Americal Journal of Optometry And Archives of American Academy of Optometry, June 1967 page 365) conclude that no corneal benefit results (even directly under the hole) from a 1.0 mm hole nor from holes as small as 25 microns. These latter holes were spark generated at a density of 3/mm.sup.2. There has thus been every reason to abandon the concept of fenestrating contact lenses, especially with small holes.
SUMMARY
According to the present invention, a contact lens has holes going part or all the way from one lens surface towards the other, in sufficient number to account for at least 5%, preferably at least 10%, more preferably at least 15%, most preferably at least 20%, optionally at least 25%, generally at least 30%, desirably at least 35% and suitably at least 40% of the area of the lens. The holes may be provided over the whole area of the lens, or in the peripheral part of the lens, or in the central region of the lens, preferably substantially uniformly over the relevant specified area, with preferably substantially no holes elsewhere. The peripheral part of the lens is deemed to be that outside a central region of 5-11 (e.g. 7-9) mm diameter, within which there are preferably fewer (e.g. under 0.7, 0.6 or 1/2mm.sup.2 altogether) or no holes. There may be at least 2000 of these holes and preferably over 5000 holes more preferably over 10.sup.4 , most preferably over 5.times.10.sup.4 possibly over 10.sup.5 such as over 5.times.10.sup.5 holes, even over 10.sup.6 holes.
The holes may be smaller than diameter 150 .mu.m (e.g. smaller than 100 .mu.m, preferably smaller than 50 .mu.m, more preferably smaller than 30 .mu.m, ideally smaller than 10 .mu.m) e.g. under 50.times.10-.sup.5 mm.sup.2 more preferably under 20.times.10-.sup.5 mm.sup.2 optionally under 10.times.10-.sup.5 mm.sup.2, desirably under 5.times.10-.sup.5 mm.sup.2, if possible under 2.times.10-.sup.5 mm.sup.2 in
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Wichterle et al "Perforated Soft Hydrogel . . . " International Eyecare, vol. 1, No. 4, Sep. 1985, pp. 315-318.
Hill et al "Respiratory Profiles of the Corneal . . . " American Journal of Optometry & Archives of American Acad. of Optometry, Jun. 1967, pp. 365-373.
R. M. Hill et al. "Respiratory Profiles of the Corneal . . . " American Jour of Optometry & Arch. of Ame. Acad of Optometry, Jun. 1967, pp. 365-379.
O. Wichterle et al. "Perforated soft hydrogel contact lenses " International Eyecare, vol. 1 No. 4, Sep. 1985, pp. 315-318.
Hamilton Ronald S.
Seden William E.
British Technology Group Ltd.
Sugarman Scott J.
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